Ultra-high molecular weight polyethylene thin-wall pipe, and method of and apparatus for manufacturing the same

ABSTRACT

A method of manufacture of an ultra-high molecular weight polyethylene thin-wall pipe which is uniform in thickness and free from a folded mark. The ultra-high molecular weight polyethylene thin-wall pipe is manufactured by supplying ultra-high molecular weight polyethylene into and melting and kneading, continuously extruding the molten substance of the ultra-high molecular weight polyethylene from a die connected to a screw of the screw extruder to form a cylindrical roughly shaped article, and diametrically expanding the cylindrical roughly extruded article by means of a tapered core and taking up.

FIELD OF THE INVENTION

This invention relates to an ultra-high molecular weight polyethylenethin-wall pipe and a method of and an apparatus for manufacturing thesame. More particularly, the present invention relates to a thin-wallpipe such as a shrinkage pipe, a pipe or a film made of ultra-highmolecular weight polyethylene and a method of and an apparatus formanufacturing the same.

Specifically, the present invention relates to an ultra-high molecularweight polyethylene shrink pipe which can be employed suitably as ashrink pipe for covering various roles, pipes and steel tubes for itsadvantages that, since, comparing with a shrink pipe obtained by aconventional blown film extrusion method, it is so thick that it can befinished by a lathe or the like and besides it is low in coefficient ofshrinkage in a longitudinal direction, it is superior in coveringefficiency and is effective to obtain an effective covering and alsosuperior in durability, and also to a method of and an apparatus formanufacturing such ultra-high molecular weight polyethylene shrink pipeefficiently.

In addition, the present invention relates to a method and an apparatusby which an ultra-high molecular weight polyethylene film suitable foran application which needs dimensional stability because, comparing witha film obtained by a conventional blown film extrusion method, it isuniform in thickness and has no folded mark at both ear edges thereofcan be obtained.

Further, the present invention relates to an ultra-high molecular weightpolyethylene thin-wall pipe wherein the ratio of an outer diameter to athickness is higher than 10 and the coefficient of thermal shrinkage islow and to a method by which an ultra-high molecular weight polyethylenethin-wall pipe of a required thickness can be manufactured readily inaccordance with an application of the same as well as to a manufacturingapparatus which can be used suitably for the method.

BACKGROUND OF THE INVENTION

Ultra-high molecular weight polyethylene is superior in abrasionresistance, self-lubrication, chemical resistance and so forth, and isapplied to various applications making use of the characteristics.

By the way, it is a conventional practice, in order to cover an outerperipheral face of a roll, a pipe, a steel tube or the like to provideweathering resistance, a chemical resistance, a durability and so forth,to cover the outer peripheral face of such roll, pipe, steel tube or thelike with a pipe, a film or the like. In this instance, it is aconventional practice to insert such roll, pipe, steel tube or the likeinto a shrink pipe or film and then make the shrink pipe or film toshrink and cover them over the roll, pipe, steel tube or the like. Insuch a case, shrink pipes or films made of TEFLON® are conventionallyused However, TEFLON® is inferior in abrasion resistance. For example,TEFLON® has a sand abrasion loss as high as five times that ofultra-high molecular weight polyethylene.

Thus, a shrink pipe or film made of ultra-high molecular weightpolyethylene has been proposed, and a method of manufacturing a shrinktube or film made of ultra-high molecular weight polyethylene, forexample, by a method which has been proposed and disclosed in JapanesePatent Laid-Open Application No. 62(1987)-122736.

However, according to the method disclosed in Japanese Patent Laid-OpenApplication No. 62(1987)-122736, a shrink tube or film duringmanufacture must necessarily be sealed to exclude internal air, thereforit is folded into a flattened outer profile by means of pinch rolls.Consequently, an ultra high molecular weight polyethylene shrink pipe orfilm obtained has folded marks at both ear edges thereof, and if theshrink tube or film is caused to shrink to cover a roll or the like,then such folded marks will remain in the shrink tube or film.Therefore, the method cannot be adopted readily for an application forwhich a high degree of accuracy is required. Further, since a shrinktube obtained by the method has a thickness equal to or less than 1 mm,it is difficult to finish it by lathe machining. Besides, since suchproduct is biaxially oriented, it is also disadvantageous in thatshrinkage in a longitudinal direction is great.

It is another conventional practice that, in order to cover an outerperipheral face of a roll, a pipe, a steel tube or the like to provide aweathering resistance, a chemical resistance, a durability and so forth,an ultra-high molecular weight polyethylene thin-wall pipe is heated to100° to 130° C. to expand the diameter thereof by thermal expansion andthen the roll, pipe, steel tube or the like is inserted into theultra-high molecular weight polyethylene thin pipe of the expandeddiameter, whereafter the thin pipe is cooled to shrink to cover theroll, pipe, steel tube or the like.

Manufacture of the ultra-high molecular weight polyethylene thin-wallpipe is conventionally made by a method of compression molding oranother method of mechanically machining a rod of ultra-high molecularweight polyethylene. However, a thin-wall pipe of an indefinite lengthcannot be obtained by those methods, and besides a high cost is requiredand it is difficult to manufacture such thin wall pipe economically.

Thus, a method of manufacturing a flexible tube made of ultra-highmolecular weight polyethylene has been proposed and is disclosed inJapanese Patent Publication Application No. 2(1990)-31270 whereinultra-high molecular weight polyethylene is melted by a screw extruderand extrusion molded from a tube die by an L/D:5 wherein a mandrel isrotated by rotation of a screw.

According to the method disclosed in Japanese Patent PublicationApplication No. 2(1990)-31270, flexible tubes of comparatively smalldiameter equal to or less then 20 mm and of comparatively thickness witha ratio of the outer diameter to the thickness equal to or less than 15can be obtained. But the method involves draw forming, so it hasdrawbacks that a pipe with an inner diameter greater than an outerdiameter of a mandrel used cannot be obtained and that a pipe obtainedgets to expand in diameter when it is heated. Further, with the method,since an outer diameter is restricted by a sizer, it is difficult toobtain an inner surface with excellent smoothness. Consequently, it isdifficult to efficiently manufacture a thin-wall pipe having a lowcoefficient of thermal shrinkage and having an inner surface withexcellent smoothness.

SUMMARY OF THE INVENTION

It is a first object of the present invention to provide an ultra-highmolecular weight polyethylene thin-wall pipe which, comparing with anultra-high molecular weight polyethylene shaped article obtained by aconventional blown film extrusion method, is uniform in thickness andfree from a folded mark and can achieve, when it is used to cover aroll, a pipe, a steel tube or the like, a covering with a high degree ofaccuracy in dimension.

It is a second object of the present invention to provide a method bywhich such ultra-high molecular weight polyethylene shaped article canbe manufactured at a high efficiency.

It is a third object of the present invention to provide an apparatuswhich can be used suitably for such manufacturing method for anultra-high molecular weight polyethylene shaped article.

It is a fourth object of the present invention to provide an ultra-highmolecular weight polyethylene shrink pipe which can be employed suitablyas a covering shrink pipe for various roles, pipes and steel tubes forits advantages that, since, comparing with a shrink pipe obtained by aconventional blown film extrusion method, it is so thick that it can befinished by a lathe or the like and besides it is low in coefficient ofshrinkage in a longitudinal direction, it is superior in coveringefficiency and is effective to obtain an effective covering and alsosuperior in durability.

It is a fifth object of the present invention to provide a method bywhich such ultra-high molecular weight polyethylene shrink pipe can bemanufactured at a high efficiency.

It is a sixth object of the present invention to provide an apparatuswhich can be used suitably for such manufacturing method for anultra-high molecular weight polyethylene shrink pipe.

It is a seventh object of the present invention to provide a method bywhich an ultra-high molecular weight polyethylene film which can beapplied suitably for an application for which a high degree of accuracyin dimension is required since it is uniform in thickness and has nofolded mark at both ear edges thereof, comparing with a film obtained bya conventional blown film extrusion method can be obtained.

It is an eighth object of the present invention to manufacture anapparatus which can be used suitably for such manufacturing method foran ultra-high molecular weight polyethylene film.

It is a ninth object of the present invention to provide an ultra highmolecular weight polyethylene thin wall pipe wherein the ratio of anouter diameter to a thickness is equal to or higher than 10 and thecoefficient of thermal shrink is low and besides the average roughnessof an inner surface is low.

It is a tenth object of the present invention to provide a method bywhich such ultra-high molecular weight polyethylene thin wall pipe of arequired thickness can be manufactured readily in accordance with anapplication thereof.

It is an eleventh object of the present invention to provide amanufacturing apparatus which can be used suitably for the manufacturingmethod for an ultra-high molecular weight polyethylene thin-wall pipe.

In order to attain the first object, according to the present invention,there is provided an ultra-high molecular weight polyethylenepipe-shaped article made of ultra-high molecular weight polyethylenehaving an intrinsic viscosity (η) of 5.0 dl/g or more, the pipe-shapedarticle being uniform in thickness and free from a folded mark.

In order to attain the second object, according to the presentinvention, there is provided a method of manufacturing an ultra-highmolecular weight polyethylene pipe-shaped article, comprising the stepsof:

supplying ultra-high molecular weight polyethylene having an intrinsicviscosity (η) of 5.0 dl/g or more into a screw extruder, and melting andkneading the ultra-high molecular weight polyethylene in the screwextruder.

The molten substance of the ultra-high molecular weight polyethylene iscontinuously extruded from a die having an L/D ratio at least 10, whichincludes an inner die connected to and rotated together with the screwof the extruder, disposed therein, and forms into a roughly cylindricalshape; and

diametrically expanding the cylindrical rough extruded article by meansof a tapered core connected to the inner die, which includes a taperedportion and a cylindrical portion continuously followed after thetapered portion, and causing the ultra-high molecular weightpolyethylene to start to be cooled to cure at the tapered core.

In order to attain the third object, according to the present invention,there is provided an apparatus for manufacturing an ultra-high molecularweight polyethylene thin-wall pipe, comprising:

an extruder including a grooved cylinder and a screw inserted in thegrooved cylinder and having a compression ratio of 1 to 2.5;

a die having an L/D ratio at least 10, including an inner die connectedto an end of the screw of the screw extruder and rotate together withthe rotation of the screw and an outer die connected to the groovedcylinder; and

a tapered core including a shaft connected to an end of the inner dieand rotated together with rotation of the inner die, a tapered portionnot rotating together with the shaft and having an increasing diameterin a downstream direction such that a maximum outer diameter thereof isat least larger than a diameter of the inner die, and a cylindricalportion provided continuously to the tapered portion.

In order to attain the fourth object, according to the presentinvention, there is provided an ultra-high molecular weight polyethyleneshrink pipe made of ultra-high molecular weight polyethylene having anintrinsic viscosity (η) of 5.0 dl/g or more, having an outer diameter(D1) of 10 mm or more and a thickness (t1) of 0.2 mm or more with aratio of the outer diameter to the thickness (D1/t1) 10 or higher, andhaving a coefficient of shrinkage of 20% or more in a diametricaldirection at 140° C.

In order to attain the fifth object, according to the present invention,there is provided a method of manufacturing an ultra-high molecularweight polyethylene shrink pipe, comprising the steps of:

supplying ultra-high molecular weight polyethylene having an intrinsicviscosity (η) of 5.0 dl/g or more into a screw extruder, and melting andkneading the ultra-high molecular weight polyethylene;

continuously extruding the molten substance of the ultra-high molecularweight polyethylene from a die having an L/D ratio at least 10, whereinan inner die connected to and rotated together with rotation of thescrew of the screw extruder, is disposed to form the extruded articleinto a roughly cylindrical rough shape; and

diametrically expanding the roughly cylindrical extruded article bymeans of a tapered core connected to the inner die such that the outerdiameter of a maximum diametrically expanding portion may be 1.2 to 3.0times of the outer diameter of the inner die, and taking up the extrudedarticle at a taking up rate five times or lower than the extruding rateat the screw extruder, and causing the ultra-high molecular weightpolyethylene to start to be cooled to cure at a tapered portion of thetapered core.

In order to attain the sixth object, according to the present invention,there is provided an apparatus for manufacturing an ultra-high molecularweight polyethylene shrink pipe, comprising:

an extruder including a grooved cylinder, and a screw inserted in thegrooved cylinder and having a compression ratio of 1 to 2.5;

a die having an L/D ratio at least 10, including an inner die connectedto an end of the screw and rotated together with rotation of the screw,and an outer die connected to the grooved cylinder; and

a tapered core including a shaft connected to an end of the inner dieand rotated together with rotation of the inner die, and a taperedforming number not rotating together with the shaft and having anincreasing diameter in a downstream direction such that a maximum outerdiameter thereof is at least 1.2 to 3.0 times the diameter of the innerdie.

In order to attain the seventh object, according to the presentinvention, there is provided a method of manufacturing an ultra-highmolecular weight polyethylene film, comprising the steps of:

supplying ultra-high molecular weight polyethylene having an intrinsicviscosity (η) of 5.0 dl/g or more into a screw extruder, and melting andkneading the ultra-high molecular weight polyethylene;

continuously extruding the molten substance of the ultra-high molecularweight polyethylene from a die having an L/D ratio at least 10, whereinan inner die connected to and rotated together with rotation of thescrew of the screw extruder is disposed in the inside of an outer die,to form a extruded article into cylindrical roughly shape; and

diametrically expanding the roughly cylindrical extruded articles bymeans of a tapered core connected to the inner die such that the outerdiameter of a maximum diametrically expanding portion may be 3 or moretimes of the outer diameter of the inner die, and taking up the extrudedarticle at a taking up rate three times or higher than the extrudingrate of the molten substance of the ultra-high molecular weightpolyethylene at the screw extruder.

In order to attain the eighth object, according to the presentinvention, there is provided an apparatus for manufacturing anultra-high molecular weight polyethylene film, comprising:

an extruder including a grooved cylinder, and a screw inserted in thegrooved cylinder and having a compression ratio of 1 to 2.5;

a die having an L/D ratio at least 10, including an inner die connectedto an end of the screw of the screw extruder and rotated together withrotation of the screw and an outer die connected to the groovedcylinder; and

a tapered core including a shaft connected to an end of the inner dieand rotated together with rotation of the inner die, and a taperedforming member not rotating together with the shaft and having anincreasing diameter at an angle of 5 to 50 degrees in a downstreamdirection such that a maximum outer diameter thereof is at least equalto or higher than 3 times the diameter of the inner die; and

a take-up unit including rolls having a width of 50 to 80% of a foldedwidth of an ultra-high molecular weight polyethylene film formed by thetapered core.

In order to attain the ninth object, according to the present invention,there is provided an ultra-high molecular weight polyethylene thin-wallpipe made of ultra-high molecular weight polyethylene having anintrinsic viscosity (η) of 5.0 dl/g or more and having an outer diameter(D2) 10 mm or more and a thickness (t2) 0.5 mm or more with a ratio ofthe outer diameter to the thickness (D2/t2) 10 or higher, and having acoefficient of shrinkage of 5% or less in a diametrical direction at100° C.

In order to attain the tenth object, according to the present invention,there is provided a method of manufacturing an ultra-high molecularweight polyethylene thin-wall pipe, comprising the steps of:

supplying ultra-high molecular weight polyethylene having an intrinsicviscosity (η) of 5.0 dl/g or more into a screw extruder, and melting andkneading the ultra-high molecular weight polyethylene;

continuously extruding the molten substance of the ultra high molecularweight polyethylene from a die having an L/D ratio at least 10,including an inner die connected to and rotated together with the screwof the screw extruder, disposed therein, to form a roughly cylindricalextruded articles; and

diametrically expanding the roughly cylindrical extruded articles bymeans of a tapered core connected to the inner die, including a taperedportion and a cylindrical portion provided continuously to the taperedportion, such that the outer diameter of a maximum diametricallyexpanding portion may be 1.2 to 3.0 times of the outer diameter of theinner die, taking up the roughly cylindrical extruded article at ataking up rate three times or lower than the extruding rate of theultra-high molecular weight polyethylene at the screw extruder, andcausing the ultra high molecular weight polyethylene to start to becooled to cure at the cylindrical portion of the tapered core.

In order to attain the eleventh object, according to the presentinvention, there is provided an apparatus for manufacturing anultra-high molecular weight polyethylene thin-wall pipe, comprising:

an extruder including a grooved cylinder, and a screw inserted in thegrooved cylinder and having a compression ratio of 1 to 2.5;

a die having an L/D ratio at least 10 including an inner die connectedto an end of the screw of the screw extruder and rotated together withrotation of the screw and an outer die connected to the groovedcylinder; and

a tapered core including a shaft connected to an end of the inner dieand rotated together with rotation of the inner die, a tapered formingmember not rotating together with the shaft and having an increasingdiameter at an angle of 5 to 50 degrees in a downstream direction suchthat a maximum outer diameter thereof is at least 1.2 to 3.0 times ofthe diameter of the inner die, and a cylindrical portion providedcontinuously to the tapered portion with a heat insulating materialinterposed therebetween.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings which are incorporated in and constitute apart of this specification, illustrate embodiments of the invention, andtogether with the description, serve to explain the principle of theinvention.

FIG. 1 is a schematic view illustrating an ultra-high molecular weightpolyethylene shrink pipe which is an embodiment of an ultra-highmolecular weight polyethylene thin-wall pipe of the present invention;

FIG. 2 is a schematic view illustrating principal steps of a method ofmanufacturing the ultra-high molecular weight polyethylene thin-wallpipe;

FIG. 3 is a schematic sectional view showing principal part of amanufacturing apparatus for the ultra-high molecular weight polyethyleneshrink pipe;

FIG. 4 is a schematic view illustrating a tapered core of themanufacturing apparatus for an ultra-high molecular weight polyethyleneshrink pipe of the present invention;

FIG. 5 is a schematic view illustrating principal steps of a method ofmanufacturing an ultra high molecular weight polyethylene film of thepresent invention;

FIG. 6 is a schematic sectional view showing principal part of amanufacturing apparatus for an ultra-high molecular weight polyethylenefilm of the present invention;

FIG. 7 is a schematic view illustrating a tapered core of themanufacturing apparatus for an ultra-high molecular weight polyethylenefilm of the present invention;

FIG. 8 is a schematic view showing an ultra-high molecular weightpolyethylene thin-wall pipe of the present invention;

FIG. 9 is a schematic sectional view showing principal part of amanufacturing apparatus for an ultra-high molecular weight polyethylenethin-wall pipe of the present invention; and

FIG. 10 is a schematic view showing a tapered core of the manufacturingapparatus for an ultra-high molecular weight polyethylene thin pipe ofthe present invention.

DETAILED DESCRIPTION OF THE DISCLOSURE

The preferred embodiments of the present invention will be described indetail below.

Ultra-high molecular weight polyethylene which is a raw material for anultra-high molecular weight polyethylene thin-wall pipe of the presentinvention consists mainly of ethylene and may be, for example,homopolymer of ethylene or copolymer which consists of ethylene as amain component and monomer copolymerizable with ethylene. The monomercopolymerizable with ethylene may be, for example, α-olefin having acarbon number of 3 or more

Such α-olefin having a carbon number of 3 or more may be, for example,propylene, 1-butene, isobutene, 1-pentene, 2-methyl-1-butene,3-methyl-1-butene, 1-hexene, 3-methyl-1-pentene, 4-methyl-1-pentene,1-heptene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene,1-octadecene or 1-icocene.

Such ultra-high molecular weight polyethylene should have an intrinsicviscosity (η) 5.0 dl/,g or higher and preferably have an intrinsicviscosity (η) of 8 to 30 dl/g so that molten substance thereof may notcause, upon molding, difference in wall thickness by twist of moltensubstance thereof by turning motion thereof together with an inner diewhich will be hereinafter described or by distortion of the inner die,and consequently, a thin-wall pipe having a uniform thickness can beobtained.

If necessary, various stabilizing agents may be mixed into the ultrahigh molecular weight polyethylene. The stabilizing agents may be, forexample, heat stabilizer such as tetrakis [methylene (3,5-di-t-butyl-4-hydroxy) hydrocinnamate] methane,distearylthiodipropionate and so forth, weathering agents such as bis(2, 2', 6, 6'-tetramethyl-4-piperidine) sebacate,2-(2-hydroxy-t-butyl-5-methylphenyl)-5-chlorobenzotriazole and so forth,and so forth. Further, an inorganic or organic dry color may be added asa coloring agent.

An ultra-high molecular weight polyethylene thin-wall pipe of thepresent invention is uniform in thickness and free from a folded mark.

The ultra-high molecular weight polyethylene thin-wall pipe may assumevarious concrete embodiment such as an ultra-high molecular weightpolyethylene shrink pipe, an ultra-high molecular weight polyethylenefilm, an ultra-high molecular weight polyethylene thin-wall pipe and soforth.

A method of and an apparatus for manufacturing such ultra-high molecularweight polyethylene thin-wall pipe are generally constituted such thatultra-high molecular weight polyethylene having an intrinsic viscosityof 5.0 dl/g or more is supplied into, and molten and kneaded, and thenthe molten substance of the ultra-high molecular weight polyethylene iscontinuously extruded from a die having a L/D ratio thereof of at least10, wherein an inner die connected to and rotated with a screw of thescrew extruder is disposed in the inside thereof, to form a roughlycylindrical shape. The roughly cylindrical extruded article isdiametrically expanded by a tapered core connected to the inner die,which includes a tapered portion and a cylindrical portion providedcontinuously to the tapered portion, and taken up by a take-up unit, theultra-high molecular weight polyethylene starts to be cooled to solidifyat the tapered core and then is cooled sufficiently by a coolingapparatus to obtain a desired thin-wall pipe.

In the following, the present invention will be described first by wayof an example of an ultra-high molecular weight polyethylene shrink pipeas a concrete form of an ultra-high molecular weight polyethylenethin-wall pipe.

An ultra-high molecular weight polyethylene shrink pipe of the presentinvention has an outer diameter (D1) of 10 mm or more as shown inFIG. 1. When the outer diameter (D1) is small, a shaft for a taperedcore is so thin accordingly that it cannot be connected readily to aninner die, but on the contrary when the outer diameter (D1) is large,there is the possibility that the cost of equipment is very high, whichis economically disadvantageous. Accordingly, a preferable outerdiameter ranges from 5 to 150 mm. Further, the thickness (t1) should be0.2 mm or more, and particularly the ultra high molecular weightpolyethylene shrink pipe is used for the covering of a roll, thethickness (t1) should preferably be 0.5 to 3 mm since machining asurface of the ultra-high molecular weight polyethylene shrink pipe canbe performed by a lathe at a following step. In addition, the ratio ofthe outer diameter to the thickness (D1/t1) should be 10 or higher andpreferably from 15 to 150 in view of economy.

An ultra-high molecular weight polyethylene shrink pipe of the presentinvention has a coefficient of shrinkage of 20 % at 140° C. in adiametrical direction, and when the shrink pipe is to be used as acovering member, the coefficient of shrinkage in a diametrical directionat 140° C. is preferably from 40 to 150% in order to assure a highcovering strength against a core member to be coated with the shrinkpipe.

Such ultra-high molecular weight polyethylene shrink pipe can bemanufactured by a method comprising the steps that

ultra-high molecular weight polyethylene having an intrinsic viscosityof 5.0 dl/g or more is supplied into, and molten and kneaded, and then

the molten substance of the ultra-high molecular weight polyethylene iscontinuously extruded from a die having a L/D ratio of at least 10,wherein an inner die connected to and rotated with a screw of the screwextruder is disposed in the inside thereof, to form a roughlycylindrical shape, and after then,

the roughly cylindrical extruded article is taken up at a taking up rateequal to or less than five times of the extruding rate of the ultra-highmolecular weight polyethylene by the screw extruder, while the diameterthereof is expanded by a tapered core connected to the inner die suchthat the inner diameter of a maximum diametrically expanded portionthereof may be 1.2 to 3.0 times of the outer diameter of the inner dieand the ultra-high molecular weight polyethylene starts to be cooled tosolidify at a tapered portion of the tapered core.

Subsequently, the manufacturing method will be described in detail inconnection with an embodiment of a manufacturing apparatus for anultra-high molecular weight polyethylene shrink pipe of the presentinvention shown in FIGS. 2 to 4.

The manufacturing apparatus for an ultra-high molecular weightpolyethylene shrink pipe shown in FIG. 2 includes as essentialcomponents a screw extruder 1, a die 2 mounted on the screw extruder 1,and a tapered core 3 provided continuously to the die 2.

The screw extruder 1 includes, as shown in FIG. 3, a grooved cylinder 4,a screw 5 inserted in the groove cylinder 4 and a hopper 6 for supplyingultra-high molecular weight polyethylene of raw material.

The inner diameter of the grooved cylinder 4 is selected suitably sothat a shrink pipe of a desired outer diameter may be obtained.Meanwhile, the grooves of the grooved cylinder 4 are formed to extendlinearly in a downstream direction and disposed by a number of 8 to 12in an equidistantly spaced relationship in a circumferential directionsuch that the length (L/D) thereof ranges from 3 to 10 and preferablyfrom 5 to 8. The shape of the grooves is preferably an angular shape ora semicircular shape so that they can reinforce a driving force forultra-high molecular weight polyethylene in the extruder. Further, thescrew 5 should have a compression ratio of 1 to 2, and preferably acompression ratio of 1.3 to 2.0. The effective length (L/D) of the screw5 normally ranges from 20 to 28 or so. The length of a compressingportion of the screw 5 ranges from 25 to 80% or so of the effectivelength (L/D). Meanwhile, the screw flight pitch normally ranges from 0.4to 0.8 or so. The speed of rotation of the screw 5 is normally 10 to 30rpm or so. Further, the hopper 6 is preferably a two-stage hopper sinceit facilitates, when the raw material is powder, back flows of air inthe cylinder 4 and can prevent occurrence of a failure in dropping ofraw material which arises from a hopper bridge.

A heating barrel 7 is disposed on a circumferential wall of the screwextruder 1 in order to melt ultra-high molecular weight polyethylenesupplied into the screw extruder 1, and a water cooling barrel 8 isdisposed in order to regulate the heating temperature by the heatingbarrel 7. The heating temperature at the screw extruder 1 is normallyadjusted to a temperature higher than a melting point of ultra-highmolecular weight polyethylene but equal to or lower than 340° C. andpreferably to a temperature from 160° to 330° C.

The die 2 mounted on the screw extruder 1 is constituted from an innerdie 9 and an outer die 10 in which the inner die 9 is inserted. Theinner die 9 is connected to an end 11 of the screw 5 of the screwextruder 1 and is rotated by rotation of the screw 5. Meanwhile, theouter die 10 is mounted at an end 12 of the heating barrel 7 of thescrew extruder 1. The die 2 has an L/D ratio at least 10 and preferablyfrom 20 to 50. Further, the inner die 9 is preferably constituted suchthat, since it is rotated by rotation of the screw 5, the outer diameterof the inner die is reduced in a tapering condition from the connectingportion thereof, and then has a fixed outer diameter at the other endportion from a mid portion thereof, and besides it is coated at asurface thereof with fluorocarbon resin in order to assure highsmoothness thereof with ultra-high molecular weight polyethylene whichcirculates in the inner die 9. A heating barrel 13 is disposed on anouter circumferential wall of the die 2 for regulating the temperatureof ultra-high molecular weight polyethylene which moves in the die 2.The heating temperature of the die 2 is normally adjusted to 160° to250° C.

In the manufacturing apparatus, the tapered core 3 shown in an enlargedview of FIG. 4 is provided continuously to the inner die 9. The taperedcore 3 includes a shaft 16 connected to an end 15 of the inner die 9,and a tapered forming member 17 loosely fitted on the shaft 16 The shaft16 connected to the end 15 of the inner die 9 is rotated together withthe inner die 9 connected to the screw 5. The outer diameter of theshaft 16 is normally smaller than the outer diameter of the inner die 9,and the length of the shaft 16 is normally equal to 10 to 50 cm or so.

Meanwhile, the tapered forming member 17 is loosely fitted on the shaft16 by means of a bearing 14 and is mounted on the shaft 16 such that itmay not rotate together with the shaft 16 The tapered forming member 17has a tapered portion 18 which is formed in an inclined relationship atan angle normally of 5 to 50 degrees and preferably of 10 to 30 degreeswith respect to an axial direction of the shaft 16 so that frictionalresistance upon diametrical expansion may be reduced to perform shapingreadily. The tapered forming member 17 further has a cylindrical portion19 provided continuously to the tapered portion 18.

A coating of fluorocarbon resin such as TEFLON (registered trade mark)is preferably applied to surfaces of the tapered portion 18 and thecylindrical portion 19 of the tapered forming member 17 so that thecoefficient of friction with an ultra-high molecular weight polyethylenemolded article may be reduced to perform molding smoothly.

The ratio in length of the tapered portion 18 to the cylindrical portion19 of the tapered forming member 17 in its axial direction is normallyset to 0.2 to 1 or so and preferably to 0.3 to 0.7 or so. Further, theouter diameter of the cylindrical portion 19 should be set at least to1.2 to 3.0 times the diameter of the inner die 9 and preferably to 1.5to 3.0 times and further preferably to 1.7 to 2.5 times the diameter ofthe inner die 9.

The method of the present invention proceeds on the manufacturingapparatus described above such that ultra-high molecular weightpolyethylene having an intrinsic viscosity (η) of 5.0 dl/g or more isfirst supplied into, molten and kneaded in the screw extruder 1, andthen the molten substance of the ultra high molecular weightpolyethylene is continuously extruded from the die 2 to form a roughlycylindrical shape, whereafter the diameter of the roughly cylindricalextruded article is expanded by the tapered core 3 such that the innerdiameter of a maximum diametrically expanded portion of the cylindricalroughly molded form may be 1.2 to 3.0 times of the outer diameter of theinner die 9 of the die 2 and preferably 1.2 to 3.0 times and furtherpreferably 1.7 to 2.5 times of the diameter of the inner die 9 so that agood shrink pipe of an appropriate thickness can be obtained. The thusdiametrically expanded shrink pipe is cooled in a cooling tank 20 andthen taken up by a take-up unit 21. The taking up rate of the take-upunit 21 is set equal to or lower then 5 times the extruding rate of theultra high molecular polyethylene by the screw extruder 1 and preferablylower than 3 times or less

The take-up unit 21 may be, for example, of the roll type, caterpillartype or belt type.

Further, in the present method, it is preferable to adjust such thatultra-high molecular weight polyethylene begins to be cooled to solidifyat the tapered portion 18 of the tapered core 3, and preferably at aportion of the tapered portion 18 at which the diameter is smaller thanthat at a mid portion of the tapered portion 18 so that an ultra-highmolecular weight polyethylene shrink pipe having a high coefficient ofshrinkage can be obtained. Such adjustment of beginning of cooling cureof an ultra-high molecular weight polyethylene shrinkage pipe can beperformed by adjusting the extruding rate of the screw extruder 1, theposition of the tapered core 3, the position of a blowing ring forcooling air or the like.

The ultra-high molecular weight polyethylene shrink pipe taken up by andformed on the take-up unit 21 is suitably cut by a cutting machine. Thecutting machine may be an automatic cutting machine such as, forexample, a shearing cutter of the round saw type or of the type using ablade.

While mainly the method of and the apparatus for manufacturing anultra-high molecular weight polyethylene shrink pipe having a circularinner profile has been described so far, the ultra-high molecular weightpolyethylene shrink pipe is not limited to that which has a circularinner profile, but may be made a pipe of an outer profile conforming toan application thereof by suitably selecting an outer profile of atapered core to be used. For example, if the outer profile of thetapered core is an angular shape or an elliptic shape, then anultra-high molecular weight polyethylene shrink pipe as a pipe of anouter shape having an inner profile corresponding to such angular orelliptic shape can be obtained.

The ultra-high molecular weight polyethylene shrink pipe of the presentinvention can be used to cover an outer profile of a tubular member byinserting the tubular member into the inside of the same and heating tocause the same to be shrunk with making use of the shrinking property ofthe same. For example, a tubular member such as a roll or a steel tubeis inserted into the ultra high molecular weight polyethylene shrinkpipe, and then the ultra-high molecular weight polyethylene shrink pipeis heated to 100° to 160° C. to cause the same to be shrunk to cover thetubular member. Heating for such covering can be performed by immersingthe ultra high molecular weight polyethylene shrink pipe into heatingfluid such as air or liquid, or by blowing hot air or flame to theultra-high molecular weight polyethylene shrink pipe.

For such covering with the ultra-high molecular weight polyethyleneshrink pipe, an outer surface of a tubular member such as a roll or asteel tube is preferably formed in advance as a rough surface so that aslide resistance between contacting faces of the shrink pipe and thetubular member may be improved.

Further, preferably an adhesive resin is interposed on an outer surfaceof a tubular member such as a roll or a steel tube before the shrinkpipe is coated on the tubular member so that the adhesive strength at aninterface between them may be improved remarkably. Such method can beperformed by thermally fusion applying powder or a film of an adhesiveresin in advance to an outer surface of the tubular member. The adhesiveresin used may be, for example, ADDMER NE060 (Mitsui PetrochemicalIndustries, Ltd., trade name) or the like or a modified product of thesame.

Subsequently, a method of and an apparatus for manufacturing anultra-high molecular weight polyethylene film as another concreteembodiment of an ultra-high molecular weight polyethylene polyethylenethin-wall pipe of the present invention will be described with referenceto FIGS. 5 to 7.

The manufacturing apparatus for an ultra-high molecular weightpolyethylene film shown in FIG. 5 includes as essential components ascrew extruder 31, a die 32 mounted on the screw extruder 31, a taperedcore member 33 provided continuously to the die 32, and a take-up unit34.

The screw extruder 31 includes, as shown in FIG. 6, a grooved cylinder35, a screw 36 inserted in the grooved cylinder 35 and a hopper 37 forsupplying ultra-high molecular weight polyethylene of raw material.

The inner diameter of the grooved cylinder 35 is selected suitably sothat a film of a desired outer diameter may be obtained The screw 36should have a compression ratio of 1 to 2.5 and preferably a compressionratio of 1.3 to 2.0. The effective length (L/D) of the screw 36 normallyranges from 20 to 28 or so. The length of a compressing portion of thescrew 36 ranges from 25 to 80% or so of the effective length (L/D).Meanwhile, the screw flight pitch normally ranges from 0.4 to 0.8 or so.The speed of rotation of the screw 36 is normally 10 to 50 rpm or so.Further, the hopper 37 is preferably a two-stage hopper since itfacilitates, when raw material in the form of powder is to be handled,back flows of air in the cylinder 35 and can prevent occurrence of afailure in dropping of raw material which arises from a hopper bridge.

A heating barrel 38 is disposed on a circumferential wall of the screwextruder 31 in order to melt ultra-high molecular weight polyethylenesupplied into the screw extruder 31, and a water cooling barrel 39 isdisposed in order to regulate the heating temperature by the heatingbarrel 38. The heating temperature at the screw extruder 31 is adjustednormally to a temperature higher than a melting point of ultra-highmolecular weight polyethylene but equal to or lower than 340° C. andpreferably to a temperature from 160° to 330° C.

The die 32 mounted on the screw extruder 31 is constituted from an innerdie 40 and an outer die 41 in which the inner die 40 is inserted Theinner die 40 is connected to an end 42 of the screw 36 of the screwextruder 31 and is rotated by rotation of the screw 36. Meanwhile, theouter die 41 is mounted at an end 43 of the heating barrel 38 of thescrew extruder 31. The die 32 has an L/D ratio at least 10 andpreferably 20 to 50. Further, the inner die 40 is preferably constitutedsuch that, since it is rotated by rotation of the screw 36, a diameterdecreases in a tapering condition from the connecting portion thereofand then has a fixed outer diameter at the other end portion from a midportion thereof, and besides it is coated at a surface thereof withfluorocarbon resin in order to assure a high slipping property thereofwith resin. An electric heater 44 is disposed on an outercircumferential wall of the die 32 for regulating the temperature ofmolten substance of ultra-high molecular weight polyethylene which movesin the die 32. The heating temperature of the die 32 is normallyadjusted to 160° to 250° C. or so.

In the manufacturing apparatus, the tapered core member 33 shown in anenlarged view of FIG. 7 is provided continuously to the inner die 40 ofthe die 32. The tapered core member 33 is loosely fitted on a shaft 47connected to an end 46 of the inner die 40. The shaft 47 connected tothe end 46 of the inner die 40 is rotated together with the inner die 40connected to the screw 36. The outer diameter of the shaft 47 isnormally smaller than the outer diameter of the inner die 40, and thelength of the shaft 47 is normally 10 to 50 cm or so.

Meanwhile, the tapered core member 33 is loosely fitted on the shaft 47by means of a bearing 49 and is mounted on the shaft 47 such that it maynot rotate together with the shaft 47.

The tapered core member 33 has a tapered portion 45 which is formed inan inclined relationship at an angle normally of 5 to 50 degrees andpreferably of 10 to 30 degrees with respect to an axial direction of theshaft 47 so that frictional resistance between the tapered core member33 and an ultra-high molecular weight polyethylene film upon diametricalexpansion may be reduced to perform a shaping operation readily. Thetapered core member 33 further has a cylindrical portion 50 providedcontinuously to the tapered portion 45.

A coating of fluorocarbon resin such as TEFLON® is preferably applied tosurfaces of the tapered portion 45 and the cylindrical portion 50 of thetapered core member 33 so that the coefficient of friction with anultra-high molecular weight polyethylene molded article may be reducedto perform molding smoothly.

The ratio in length of the tapered portion 45 to the cylindrical portion50 of the tapered core member 33 in its axial direction is normally setto 0.2 to 2 or so and preferably to 0.5 to 1.0 or so. Further, themaximum outer diameter of the tapered portion 45, that is, the outerdiameter of the cylindrical portion 50, should be set at least to 3.0times or more than the diameter of the inner die 40 and preferably to 4times or more and further preferably to 5 to 7 times of the diameter ofthe inner die 40.

The manufacturing apparatus includes the take-up unit 34 as shown inFIG. 5. The take-up unit 34 includes 2 to 4 pairs, preferably 4 pairs,of rolls 51 disposed serially in a taking off direction of an ultra-highmolecular weight polyethylene film. The rolls 51 preferably have a widthof 50 to 80%, preferably of 70 to 80%, of a folding width of anultra-high molecular weight polyethylene film shaped by the tapered coremember 33 so that a sufficient taking up force may be obtained and afilm which is uniform without having a wrinkle and has no folded mark atboth ear edges thereof may be obtained.

In the manufacturing apparatus described above, ultra-high molecularweight polyethylene having an intrinsic viscosity (η) of 5.0 dl/g ormore is first supplied into, molten and kneaded in the screw extruder31, and then the molten substance of the ultra-high molecular weightpolyethylene is continuously extruded from the die 32 to form a roughlycylindrical shape, whereafter the diameter of the roughly cylindricalextruded articles is expanded by the tapered core member 33 such thatthe inner diameter of a maximum diametrically expanded portion of theroughly cylindrical extruded articles may be 3 times or more than theouter diameter of the inner die 40 of the die 32 and preferably 4 timesor more and further preferably 5 times or more than the diameter of theinner die 40 so that a good film of an appropriate thickness can beobtained. In this instance, in case the maximum outer diameter of thetapered portion 45, that is, the outer diameter of the cylindricalportion 50, is set to 5 times or more than the diameter of the inner die40, a small hole may be formed at a location of the connecting portionat which the shaft 47 is connected to the end 46 of the inner die 40 sothat compressed air may be blown in through the small hole to promotethe diameter expanding operation.

The thus diametrically expanded film is cooled in a cooling tank 52 andthen taken up by the take-up unit 34. The taking off rate of the take-upunit 34 is adjusted equal to or higher than 3 times and preferably to 3to 20 times the extruding rate of the molten substance of the ultra-highmolecular weight polyethylene by the screw extruder 31.

The ultra-high molecular weight polyethylene film of the presentinvention taken up by and formed on the take-up unit 34 is obtained inthe form of a tube The ultra-high molecular weight polyethylene film inthe form of a tube may be used as a film in the form of a tube as it isor may be cut at a portion thereof by a cutting machine and developed sothat it may be used as a biaxially oriented film which has a great widthand is free from a folded mark. The cutting machine may be a popularcutting machine such as, for example, a cutter blade. Or else, abiaxially oriented film obtained may be divided into belts or tapeselongated in a direction of a flow so that they may be used as basepaper for stretchable tapes.

Subsequently, a method of and an apparatus for manufacturing anultra-high molecular weight polyethylene thin-wall pipe as a furtherconcrete embodiment of an ultra-high molecular weight polyethylenethin-wall pipe of the present invention will be described with referenceto FIGS. 8 to 10.

An ultra-high molecular weight polyethylene thin-wall pipe of thepresent invention has an outer diameter (D2) of 10 mm or more as shownin FIG. 8, and has a thickness (t2) of 0.5 mm or more, and in a rangewithin which it can be shaped economically at a high productivity,preferably the outer diameter (D2) ranges from 25 to 100 mm and thethickness (t2) ranges from 1 to 5 mm. Further, the ratio of the outerdiameter to the thickness (D2/t2) should be 10 or higher and preferably15 to 50 so that a pipe having a high rigidity may be obtained. Further,the surface roughness of an inner face of the pipe in an extrudingdirection is equal to or less than 1.0 in average roughness and equal toor less than 5 in maximum roughness (Rmax). Preferably, the averageroughness (Ra) is equal to or less than 0.5 and the maximum roughness(Rmax) is equal to or less than 5 so that the flowing resistance thereofwhen it is used as a conveying hose for powder or fluid may besuppressed to a low level.

The ultra-high molecular weight polyethylene thin-wall pipe has acoefficient of shrinkage in a diametrical direction which is 5% or lowerat 100° C., and when it is used in an environment of a high temperature,or when the dimension of the inner diameter is very significant on anapplication and a function of the pipe, the coefficient of shrinkage ofthe pipe in a diametrical direction at 100° C. is preferably from 0 to3%.

The ultra-high molecular weight polyethylene thin-wall pipe can bemanufactured in accordance with such a process that the ultra-highmolecular weight polyethylene is supplied into, molten and kneaded in ascrew extruder and then the molten substance of the ultra-high molecularweight polyethylene is continuously extruded from a die connected to ascrew of the extruder to form a roughly cylindrical shape, whereafterthe roughly cylindrical extruded articles is taken up whilediametrically expanding the same by means of a tapered core.

An apparatus for manufacturing the ultra-high molecular weightpolyethylene thin-wall pipe basically has the same construction as thatof the apparatus shown in FIGS. 2 and 3. In particular, themanufacturing apparatus basically includes a screw extruder, a diemounted on the screw extruder, a tapered core member providedcontinuously to the die, and a take-up unit The screw extruder issimilar to those for an ultra-high molecular weight polyethylene shrinkpipe and an ultra-high molecular weight polyethylene film describedhereinabove in that it includes, as shown in FIG. 9, a grooved cylinder65, a screw 66 inserted in the grooved cylinder 65, and a hopper 67 forsupplying ultra-high molecular weight polyethylene of raw material.

The inner diameter of the grooved cylinder 65 is selected suitably sothat a thin-wall pipe of a desired outer diameter may be obtained. Thescrew 66 should have a compression ratio of 1 to 2.5, and preferably acompression ratio of 1.3 to 2.0. The effective length (L/D) of the screw66 normally ranges from 20 to 28 or so. The length of a compressingportion of the screw 66 ranges from 25 to 80% or so of the effectivelength (L/D). Meanwhile, the screw flight pitch normally ranges from 0.4to 0 8 or so. The speed of rotation of the screw 66 is normally 10 to 50rpm or so. Further, the hopper 67 is preferably a two-stage hopper sinceit facilitates, when raw material in the form of powder is to behandled, back flows of air in the cylinder 65 and can prevent occurrenceof a failure in dropping of raw material which arises from a hopperbridge.

A heating barrel 68 is disposed on a circumferential wall of the screwextruder in order to melt ultra-high molecular weight polyethylenesupplied into the screw extruder, and a water cooling barrel 69 isdisposed in order to regulate the heating temperature by the heatingbarrel 68. The heating temperature at the screw extruder is adjustednormally to a temperature higher than a melting point of ultra-highmolecular weight polyethylene but equal to or lower than 340° C. andpreferably to a temperature from 160° to 330° C.

The die 62 mounted on the screw extruder is constituted from an innerdie 70 and an outer die 71 in which the inner die 70 is inserted. Theinner die 70 is connected to an end 72 of the screw 66 of the screwextruder and is rotated by rotation of the screw 66. Meanwhile, theouter die 71 is mounted at an end 73 of the heating barrel 68 of thescrew extruder. The die 62 has an L/D ratio at least 10 and preferably20 to 50. Further, the inner die 70 is preferably constituted such that,since it is rotated by rotation of the screw 66, it decreases inthickness in a tapering condition from the connecting portion thereofand then has a fixed outer diameter at the other end portion from a midportion thereof and besides it is coated at a surface thereof withfluorocarbon resin in order to assure a high slipping property thereofwith ultra-high molecular weight polyethylene which passed through inthe inside thereof. A heating barrel 74 is disposed on an outercircumferential wall of the die 62 for regulating the temperature ofmolten substance of ultra-high molecular weight polyethylene which movesin the die 62. The heating temperature of the die 62 is normallyadjusted to 160° to 250° C. or so.

In the manufacturing apparatus, the tapered core member 63 shown in anenlarged view of FIG. 10 is provided continuously to the inner die 70 ofthe die 62. The tapered core member 63 includes a shaft 77 connected toan end 76 of the inner die 70, and a tapered forming member 78 looselyfitted on the shaft 77. The shaft 77 connected to the end 76 of theinner die 70 is rotated together with the inner die 70 connected to thescrew 66. The outer diameter of the shaft 77 is normally smaller thanthe outer diameter of the inner die 70, and the length of the shaft 77is normally 10 to 50 cm or so.

Meanwhile, the tapered forming member 78 is loosely fitted on the shaft77 by means of a bearing 79 and is mounted on the shaft 77 such that itmay not rotate together with the shaft 77. The tapered forming member 78has a tapered portion 80 which is formed in an inclined relationship atan angle normally of 5 to 50 degrees and preferably of 10 to 30 degreeswith respect to an axial direction of the shaft 77 so that frictionalresistance between the tapered shaping member 78 and an ultra-highmolecular weight polyethylene thin-wall pipe upon diametrical expansionmay be adjusted to a range within which a shaping operation can beperformed readily. The tapered forming member 77 further has acylindrical portion 81 provided continuously to the tapered portion 80.

The tapered portion 80 of the tapered forming member 78 preferably hasconvex and concave portions on a surface thereof so that the contactarea thereof with a roughly molded form may be reduced to delay coolingand solidifying of the roughly shaped article such that the pipe made ofthe ultra-high molecular weight polyethylene may be cooled at thecylindrical portion 81 so as to obtain a thin-wall pipe having a lowcoefficient of thermal shrinkage. Such convex and concave portionsformed on the surface of the tapered portion 80 of the tapered formingmember 78 may be provided, for example, by forming convex and concaveportions in the form of a satin crape finish on the surface or bycutting several grooves in a direction perpendicular to the axis of thetapered portion 80 like annular rings.

Meanwhile, the cylindrical portion 81 of the tapered forming member 78has a smooth surface

Further, in order to prevent that the tapered portion 80 of the taperedforming member 78 is deprived of heat by the cylindrical portion 81immersed in and cooled by a cooling water tank to drop the temperaturethereof so that cooling and solidify of a roughly molded form begins atthe tapered portion 80, but to allow cooling cure of the roughly moldedform to be delayed so that cooling and solidifying may be begun at thecylindrical portion 81, the tapered portion 80 and the cylindricalportion 81 are connected to each other with a heat insulating material82 interposed therebetween in order to thermally isolate the taperedportion 80 and the cylindrical portion 81 from each other. The heatinsulating material 82 may be, for example, a teflon® sheet.

A coating of fluorocarbon resin such as teflon® is preferably applied tosurfaces of the tapered portion 80 and the cylindrical portion 81 of thetapered forming member 78 so that the coefficient of friction with anultra-high molecular weight polyethylene molded form may be reduced toperform molding smoothly.

The ratio in length of the tapered portion 80 to the cylindrical portion81 of the tapered shaping member 78 in its axial direction is normallyset to 0.2 to 1 or so and preferably to 0.3 to 0.7 or so. Further, themaximum outer diameter of the tapered portion 80, that is, the outerdiameter of the cylindrical portion 81, should be set at least to 1.2 to3 times the diameter of the inner die 70 and preferably to 1.5 to 3.0times and further preferably to 1.7 to 2.5 times the diameter of theinner die 70.

The present manufacturing apparatus includes the take-up unit. Thetake-up unit includes 2 to 4 pairs, preferably 4 pairs, of rollsdisposed serially in a taking up direction of an ultra-high molecularweight polyethylene thin pipe.

In the manufacturing apparatus described above, ultra-high molecularweight polyethylene having an intrinsic viscosity (η) of 5.0 dl/g ormore is first supplied into, molten and kneaded in the screw extruder,and then the molten substance of the ultra-high molecular weightpolyethylene is continuously extruded from the die 62 to form a roughlycylindrical shape, whereafter the diameter of the roughly cylindricalextruded article is expanded by the tapered core 63 such that the innerdiameter of a maximum diametrically expanded portion of the roughlycylindrical extruded articles may be 1.2 to 3 times and preferably 1.5to 3 times and further preferably 1.7 to 2.5 times as the diameter ofthe inner die 70 so that a good film of an appropriate thickness can beobtained.

In this instance, the manufacturing apparatus is adjusted such that athin-wall pipe to be shaped by the tapered core member 63 may begin tobe cooled to cure at the cylindrical portion 81 of the tapered coremember 63 so that a pipe having a low coefficient of thermal shrinkagemay be obtained. Such adjustment of the cooling and solidifying startingpoint to the location of the cylindrical portion 81 can be performed bysuitably selecting the extruding rate of the die 62, the distancebetween the tapered portion 80 of the tapered core member 63 and theinner die 70, or the position at which cooling by air or water takesplace.

The thus diametrically expanded thin-wall pipe is cooled in the coolingtank and then taken up by the take-up unit. The taking up rate of thetake-up unit is adjusted 3 times or lower the extruding rate of themolten substance of the ultra-high molecular weight polyethylene by thescrew extruder and preferably 1.1 to 2 times so that a slack does notoccur at the roughly extruded article and a shaping operation is easyand besides an ultra-high molecular weight polyethylene thin pipe havinga low coefficient of thermal shrinkage in its longitudinal direction maybe obtained.

The ultra-high molecular weight polyethylene thin pipe taken up by andformed on the take-up unit can be cut with a required length by acutter. The cutter may be a popular apparatus such as a shearing cutteremploying a round saw or a blade.

Further, the ultra-high molecular weight polyethylene thin pipe of thepresent invention can be partially cut away and developed into a sheet,which is then cut into belts or tapes elongated in a direction of a flowso that they may be used as base threads for stretchable yarns.

EXAMPLES

In the following, the present invention will be described in detail inconnection with examples of the present invention and comparativeexamples. However, the present invention shall not be restricted by theexamples at all unless the spirit and scope of the present invention areexceeded.

EXAMPLE 1

Ultra-high molecular weight polyethylene shrink pipes were manufacturedusing an apparatus which has the same construction as that of themanufacturing apparatus for a shrink pipe shown in FIG. 2 and whereinspecifications of the components are such as follows:

    ______________________________________                                        Extruder:                                                                     outer diameter of screw 30     mmφ                                        effective length (L/D) of screw                                                                       22                                                    flight pitch            18     mm                                             compression ratio of screw                                                                            1.8                                                   Die:                                                                          length of die           750    mm                                             inner diameter of outer die at exit                                                                   20     mmφ                                        of die                                                                        effective length (L/D) of die                                                                         37.5                                                  outer diameter of inner die                                                                           15     mmφ                                        Tapered core connected to end of inner die: having                            tapered portion and cylindrical portion integrally                            shaped from aluminum metal and coated with teflon ®                       at surface thereof.                                                           tapered portion maximum diameter                                                                             26 mmφ                                                     length         50 mm                                          cylindrical portion                                                                           outer diameter 26 mmφ                                                     length         80 mm                                          ______________________________________                                    

The apparatus further includes an air ring for cooling a roughly moldedform of resin, a cooling water tank, a take-up unit of the roll type anda pipe cutting machine.

Powder resin of ultra-high molecular weight polyethylene (η): 15.1 dl/g,melting point: 136° C., bulk specific gravity: 0.43 g/cc) (MitsuiPetrochemical Industries, Ltd., HIZEX MILLION 240M) was supplied intothe apparatus, and the temperatures at the water cooling barrel (C₁) andthe heating barrel which was divided into three zones (C₂, C₃ and C₄)were adjusted to 20° C., 290° C., 330° C. and 330° C., respectively.Further, the temperatures of the die which was divided into three zones(D₁, D₂ and D₃) were adjusted to 230° C., 180° C. and 170° C.,respectively. In this condition, the ultra-high molecular weightpolyethylene was extrusion molded into a roughly molded form at thenumber of revolution of the screw of 12 rpm and at the extruding rate of18 cm/min. At the exit of the die, the roughly cylindrical extrudedarticle was cut in the extruding direction by a knife and passed throughthe cooling water tank. Then, the extruded article was introduced intothe take-up unit of the roll type including rolls rotating at the speedof 30 cm/min. After then, the cutting operation by means of the knifewas stopped, and the diameter of the extruded article was expanded bythe tapered portion of the tapered core, and cooling air was blown fromthe air ring to the extruded article. The amount of the cooling air wasadjusted so that cooling cure of the extruded article might start at anintermediate portion of the tapered portion. Thus, shrink pipes made ofthe ultra-high molecular weight polyethylene wherein the outer diameteris 27.0 mmφ while the inner diameter is 25.5 mmφ and the expansion ratio(inner diameter ratio) is 1.7 were manufactured.

Coefficients of thermal shrinkage of the ultra-high molecular weightpolyethylene shrinkage pipes were measured by the following method.Results are shown in Table 1.

Measurement of Coefficient of Thermal Shrinkage

Every specimen was heated for one hour at 140° C. in an air oven, andafter lapse of 24 hours at 23° C. a coefficient of shrinkage of an innerdiameter in a diametrical direction was measured and decided as an indexto a coefficient of thermal contraction.

    coefficient of thermal shrinkage (%)={(dimension before heating-dimension after heating)/dimension before heating}×100

EXAMPLE 2

Ultra-high molecular weight shrink contraction pipes having an outerdiameter of 44.9 mmφ and an inner diameter of 44 mmφ were manufacturedin the same conditions as those in the Example 1 except that anothertapered core having an outer diameter of 45 mmφ (expansion ratio of 3)was used, and coefficients of thermal shrinkage of them were measured.Results are shown in Table 1.

Comparative Example 1

Pipes made of ultra-high molecular weight polyethylene having an outerdiameter of 17.7 mmφ and an inner diameter of 14.0 mmφ (expansion ratio:0.93) were manufactured in the same conditions as those in the Example 1except that no tapered core was used and the taking up rate was setdifferently to 20 cm/min, and coefficients of thermal shrinkage of themwere measured. Results are listed in Table 1.

Comparative Example 2

Molding of shrink pipes was attempted in the same conditions as those inthe Example 1 except that polyethylene powder resin having an intrinsicviscosity (η) of 3.5 dl/g, a density of 0.950 g/cc and a bulk specificgravity of 0.38 g/cc (Mitsui Petrochemical Industries, Ltd., HIZEX8000FP) was used and the heating temperatures at the zones C₁, C₂, C₃and C₄ of the extruder were adjusted to 20° C., 210° C., 230° C. and230° C., respectively. However, since the resin was turned together withrotation of the inner die, it was difficult to manufacture roughlyshaped articles, and consequently, no shrink pipes were manufactured.

                  TABLE 1                                                         ______________________________________                                                                 Compara-  Compara-                                           Example          tive      tive                                               1      Example 2 Example 1 Example 2                                  ______________________________________                                        Outer Diameter                                                                          27.0     44.9      17.7    Shaping                                  (D) (mm)                             Impossible                               Inner Diameter                                                                          25.5     44.0      14.0                                             (D) (mm)                                                                      Thickness 0.75     0.45      1.85                                             (t) (mm)                                                                      (D)/(t)   36.0     99.8      9.6                                              Expansion 1.7      2.9       0.93                                             Ratio (Inner                                                                  Dia.) (times)                                                                 Coefficient                                                                             30       91        3.6                                              of Thermal                                                                    Shrinkage (%)                                                                 ______________________________________                                    

EXAMPLE 3

Ultra-high molecular weight polyethylene films were manufactured using amanufacturing apparatus for an ultra-high molecular weight polyethylenefilm which has such structure as shown in FIG. 5 and includes a screwextruder wherein various portions have the following specifications:

    ______________________________________                                        outer diameter of screw                                                                              30    mmφ                                          effective length (L/D) of screw                                                                      22                                                     flight pitch           18    mm (fixed)                                       compression ratio of screw                                                                           1.8                                                    ______________________________________                                    

a die wherein various portions have the following specifications:

    ______________________________________                                        length of pipe die     750    mm                                              inner diameter of outer die                                                                          20     mmφ                                         at exit of die                                                                effective length (L/D) of die                                                                        37.5                                                   outer diameter of inner die                                                                          15     mmφ                                         ______________________________________                                    

a tapered core including a tapered portion connected to an end of theinner die and having an increasing diameter at an angle of 15/100 (11.7degrees) with respect to a shaft and further having a maximum outerdiameter of 60 mmφ and a length of 110 mm, and a cylindrical portionhaving an outer diameter of 60 mmφ and a length of 200 mm and having afluorocarbon resin coating applied to a surface thereof, a cooling watertank, a take-up unit of the roll type including four pairs of rubberrolls having an outer diameter of 150 mmφ and a width of 65 mm, and atake-up unit.

Ultra high molecular weight polyethylene in the form of powder having anintrinsic viscosity (η) of 15.4 dl/g, a melting point of 136° C. and abulk specific gravity of 0.43 g/cc was supplied into the manufacturingapparatus, and the preset temperatures at a water cooling barrel (C₁)and the heating barrel which was divided into three zones (C₂, C₃ andC₄) were adjusted to 20° C., 290° C., 335° C. and 335° C., respectively.Further, the preset temperatures at three zones (D₁, D₂ and D₃) of thedie were adjusted to 230° C., 180 ° C. and 168° C., respectively. Inthis condition, the ultra-high molecular weight polyethylene wasextrusion molded, while being molten and kneaded, into a roughlycylindrical extruded article at the number of revolution of the screw of10 rpm and at the extruding rate of 15 cm/min. The roughly cylindricalextruded article was cut by a knife located at the exit of the die andpassed through the cooling water tank. Then, the roughly extrudedarticle was introduced into the take-up unit in which the 4 pairs ofrubber rolls were rotating at the speed of 20 cm/min. After then, thecutting operation of the extruded article was stopped, and the diameterof the extruded article was expanded into the profile of a pipe by thetapered portion of the tapered core. Subsequently, the thusdiametrically expanded extruded article was advanced, at a portionthereof of a length of 200 mm from an end of the cylindrical portionthereof, into the cooling water tank so that the extruded article in theprofile of a pipe may be cooled to cure at the cylindrical portion ofthe tapered core. The taking up rate of the take-up unit was adjusted to2 m/min. Consequently, ultra-high molecular weight polyethylene filmshaving a thickness of 55 μm and free from a folded mark at both earedges thereof were obtained.

The ultra-high molecular weight polyethylene films were applied to atensile test and coefficients of thermal shrinkage were measured inaccordance with the following method. Results are listed in Table 2.

Tensile Test

A tensile strength at breaking point (TS: kg/cm²) and an elongation (EL:%) of specimen were measured for both of a longitudinal direction (MD)and a transverse direction (TD) in the following testing conditions:

    ______________________________________                                        shape of specimen    JIS K6781                                                chucking distance     86 mm                                                   stretching speed     200 mm/min                                               temperature          23° C.                                            ______________________________________                                    

Coefficient of Thermal Shrinkage

Specimen was heated for one hour at 130° C. in an air oven, and afterlapse of 24 hours at 23° C., coefficients of thermal shrinkage both in alongitudinal direction (MD) and a transverse direction (TD) weremeasured in accordance with the following expression:

    coefficient of thermal shrinkage (%)={(dimension before heating-dimension after heating)/dimension before heating}×100

EXAMPLE 4

Ultra-high molecular weight polyethylene films having a thickness of 58μm and free from a folded mark at both ear edges thereof weremanufactured in the same conditions as those in the Example 3 exceptthat a further tapered core having a tapered portion having a maximumouter diameter of 75 mmφ and a take-up unit including rolls having awidth of 90 mm were used and the taking up rate of the take-up unit wasset to 1.5 mm/min, and a tensile test was conducted for them andcoefficients of thermal shrinkage of them were measured. Results areshown in Table 2.

Comparative Example 3

Ultra-high molecular weight polyethylene films having a thickness of 40μm and free from a folded mark at both ear edges thereof weremanufactured in the same conditions as those in the Example 3 exceptthat a different tapered core having a tapered portion having a maximumouter diameter of 40 mmφ and a different take-up unit including rollshaving a width of 50 mm were used and the taking up rate of the take-upunit was set to 4 m/min, and a tensile test was conducted for them andcoefficients of thermal shrinkage of them were measured. Results areshown in Table 2.

Comparative Example 4

Manufacture of polyethylene films was attempted in the same conditionsas those in the Example 3 except that, in place of ultra-high molecularweight polyethylene, powder of general purpose polyethylene resin havingan intrinsic viscosity (η) of 3.5 dl/g, a density of 0.950 g/cc and abulk specific gravity of 0.38 g/cc (Mitsui Petrochemical Industries,Ltd., HIZEX 8000FP) was used and the heating temperatures at the watercooling barrel (C₁) and three zones (C₂, C₃ and C₄) of the heatingbarrel of the extruder were adjusted to 20° C., 210° C., 230° C. and230° C., respectively. However, since a roughly molded form in the formof a pipe was turned together with rotation of the inner die due to alow melt viscosity of the resin, no films were manufactured. Results areshown in Table 2.

Comparative Example 5

Ultra-high molecular weight polyethylene films were manufactured in thesame conditions as those in the Example 3 except that a take-up unitincluding rolls having a width of 100 mm was used, and a tensile testwas conducted for them and coefficients of thermal shrinkage of themwere measured. Results are shown in Table 2.

Comparative Example 6

Manufacture of ultra-high molecular weight polyethylene films wasattempted in the same conditions as those in the Example 3 except that atake-up unit including rolls having a width of 45 mm was used. However,the taking up force was not able to stand frictional resistance upondiametrical expansion of a roughly molded form by the tapered core, andconsequently, no films were manufactured.

                                      TABLE 2                                     __________________________________________________________________________                Example                                                                            Example                                                                            Comparative                                                                          Comparative                                                                          Comparative                                                                          Comparative                        Evaluation Items                                                                       Unit                                                                             3    4    Example 3                                                                            Example 4                                                                            Example 5                                                                            Example 6                          __________________________________________________________________________    (η) of Raw                                                                         dl/g                                                                             15.4 15.4 15.4   3.5    15.4   15.4                               Material                                                                      Core Maximum                                                                              4    5    2.7    4      4      4                                  Dia./Inner Die                                                                Dia                                                                           Taking Up Rate/                                                                           13   10   27     13     13     13                                 Roughly Shaped                                                                Article Speed                                                                 Roll Width  65   90   50     65     100    45                                 Evaluation of                                                                          -- Good Good Good   Shaping                                                                              Folded Take-off                           Shapeability                 Impossible                                                                           Marks on                                                                             Incomplete                                                             Both Ears                                 TS                                                                            MD          1250 1100 1860   --     1300   --                                 TD          1070 1550 920           1040                                      EL                                                                            MD          160  110  30     --     90     --                                 TD          100  80   220           150                                       Coefficient                                                                   of Thermal                                                                    Shrinkage                                                                     MD          37   14   55     --     35     --                                 TD          28   31   6             29                                        __________________________________________________________________________

EXAMPLE 5

Ultra-high molecular weight polyethylene thin-wall pipes weremanufactured using an apparatus which has the same construction as thatof the manufacturing apparatus for a thin pipe shown in FIGS. 2 and 9and wherein specifications of the components are such as follows:

    ______________________________________                                        Extruder:                                                                     outer diameter of screw 30     mm0                                            effective length (L/D) of screw                                                                       22                                                    flight pitch            18     mm                                             compression ratio of screw                                                                            1.8                                                   Die:                                                                          length of die           750    mm                                             inner diameter of outer die at exit                                                                   20     mm0                                            of die                                                                        effective length (L/D) of die                                                                         37.5                                                  outer diameter of inner die                                                                           15     mm0                                            ______________________________________                                    

Tapered core shown in FIG. 10, connected to end of inner die: havingtapered portion diametrically expanding at angle of 14/100 (8 degrees)with respect to shaft and coated with TEFLON® at surface thereof.TEFLON® sheet of 1 mm thick is held between tapered portion andcylindrical portion as heat insulating material.

    ______________________________________                                        tapered portion                                                                              maximum diameter                                                                             26     mmφ                                                 length         50     mm                                       cylindrical portion                                                                          outer diameter 26     mmφ                                                 length         150    mm                                       ______________________________________                                    

The apparatus further include a cooling water tank, a take-up unit ofthe roll type and a pipe cutting machine.

Powder resin of ultra-high molecular weight polyethylene (η): 15.4 dl/g,melting point: 136° C., bulk specific gravity: 0.43 g/cc) (MitsuiPetrochemical Industries, Ltd., HIZEX MILLION 240M) was supplied intothe apparatus, and the temperatures at the water cooling barrel (C₁) andthe heating barrel which was divided into three zones (C₂, C₃ and C₄)were adjusted to 20° C., 290° C., 330° C. and 330° C., respectively.Further, the temperatures of the die which was divided into three zones(D₁, D₂ and D₃) were adjusted to 230° C., 180° C. and 170° C.,respectively.

In this condition, the ultra-high molecular weight polyethylene wasextrusion molded into a extruded article at the number of revolution ofthe screw of 20 rpm and at the extruding rate of 30 cm/min. At the exitof the die, the cylindrical extruded article was cut in the extrudingdirection by a knife and passed through the cooling water tank. Then,the roughly molded form was introduced into the take-up unit of the rolltype including rolls rotating at the speed of 40 cm/min. After then, thecutting operation by means of the knife was stopped, and the diameter ofthe extruded article was expanded by the tapered portion of the taperedcore. Subsequently, the thus diametrically expanded extruded article wasadvanced, at a portion thereof of a length of 100 mm from an end of thecylindrical portion thereof, into the cooling water tank. Thus,ultra-high molecular weight polyethylene thin-wall pipes having an outerdiameter of 27.8 mmφ and an inner diameter of 25.6 mmφ were obtained.

Coefficients of thermal shrinkage and surface roughnesses of theultra-high molecular weight polyethylene thin-wall pipes were measuredin accordance with the following method. Results are shown in Table 3.

Measurement of Coefficient of Thermal Shrinkage

Every specimen was heated for one hour at 100° C. in an air oven, and acoefficient of shrinkage of an inner diameter in a diametrical directionafter lapse of 24 hours at 23° C. was measured and decided as an indexto a coefficient of thermal shrinkage.

    coefficient of thermal shrinkage (%)={(dimension before heating-dimension after heating)/dimension before heating}×100

Surface Roughness

Surface roughnesses of inner and outer diameters of every thin-wall pipewere measured in conformity to JIS B0601.

Ra: center line average roughness (μm)

Rmax: maximum roughness (μm)

EXAMPLE 6

Ultra-high molecular weight polyethylene thin-wall pipes having an outerdiameter of 45.7 mmφ and an inner diameter of 44.5 mmφ were manufacturedin the same conditions as those in the Example 5 except that a taperedcore having an outer diameter of 45 mmφ was used, and coefficients ofthermal shrinkage and surface roughnesses of them were measured. Resultsare shown in Table 3.

EXAMPLE 7

Thin-wall pipes made of ultra-high molecular weight polyethylene andhaving an outer diameter of 45.5 mmφ and an inner diameter of 44.2 mmφwere manufactured in the same conditions as those in the Example 5except that a tapered core having an outer diameter of 45 mmφ was usedand a extruded article was advanced, at a portion thereof of a length of120 mm from an end of the cylindrical portion of the tapered core, intothe cooling water tank so that the cooling cure point of the roughlyshaped article might be at the tapered portion, and coefficients ofthermal shrinkage and surface roughnesses of them were measured. Resultsare shown in Table 3.

Comparative Example 7

Pipes made of ultra-high molecular weight polyethylene and having anouter diameter of 18.1 mmφ and an inner diameter of 14.3 mmφ weremanufactured in the same conditions as those in the Example 5 exceptthat no tapered core was used and the taking up rate was set differentlyto 35 cm/min, and coefficients of thermal shrinkage and surfaceroughnesses of them were measured. Results are shown in Table 3.

Comparative Example 8

Molding of thin-wall pipes was attempted in the same conditions as thosein the Example 5 except that polyethylene powder resin having anintrinsic viscosity (η) of 3.5 dl/g, a density of 0.950 g/cc and a bulkspecific gravity of 0.38 g/cc (Mitsui Petrochemical Industries, Ltd.,HIZEX 8000FP) was used as raw material and the heating temperatures atthe zones C₁, C₂, C₃ and C₄ of the extruder were adjusted to 20 ° C.,210° C., 230° C. and 230° C., respectively. However, since the moltenresin was turned together with rotation of the inner die, it wasdifficult to manufacture roughly shaped articles, and consequently, noshrink pipes were manufactured Results are shown in Table 3.

                  TABLE 3                                                         ______________________________________                                                             Comparative                                                          Examples   Examples                                               Evaluation Items                                                                            5      6      8    7     8                                      ______________________________________                                        (η) of Raw Material                                                                     15.4   15.4   15.4 15.4  3.5                                    Ultra-high molecular                                                          weight Polyethylene                                                           (dl/g)                                                                        Outer Diameter (D)                                                                          27.8   45.7   45.5 18.1  Shaping                                (mm)                                   Impossible                             Inner Diameter (mm)                                                                         25.6   44.5   44.2 14.3                                         Thickness (t) (mm)                                                                          1.1    0.6    0.65 1.9                                          D/t           25     76     70   10                                           Expansion Ratio                                                                             1.7    3.0    2.9  0.95                                         (Inner Dia.) (times)                                                          Coefficient of Thermal                                                                      0.2    2.8    8.2  -0.1                                         (%) -Shrinkage (Inner Dia.)                                                   Surface Roughness (μm)                                                     Average Roughness                                                             (Ra)                                                                          Inner Surface 0.26   0.23   0.41 1.33                                         Outer Surface 1.47   1.72   2.55 1.58                                         Maximum Roughness                                                             (Rmax)                                                                        Inner Surface 2.0    1.6    2.4  8.3                                          Outer Surface 9.3    10.8   15.2 9.1                                          ______________________________________                                    

Since an ultra-high molecular weight polyethylene thin-wall pipe of thepresent invention is uniform in thickness and free from a folded mark,when a roll, a pipe, a steel tube or the like is coated with thisthin-wall pipe, a coating with a high degree of accuracy can beobtained.

Further, a method of and an apparatus for manufacturing can manufacturethe thin-wall pipe as described above at a high efficiency and have alarge merit in industrial practice.

An ultra-high molecular weight polyethylene shrink pipe of the presentinvention is thick and allows finish working thereof by means of a latheor the like and besides is low in coefficient of shrinkage in alongitudinal direction, comparing with a shrink pipe obtained by aconventional blown film extrusion method. Accordingly, the coatingefficiency is high and an coating can be obtained economically. Further,since ultra-high molecular weight polyethylene is superior in abrasionresistance, self-lubrication and chemical resistance, and particularlysuperior in abrasion resistance to fluorocarbon resins, the ultra-highmolecular weight polyethylene shrink pipe of the present invention issuperior in durability. Consequently, the ultra-high molecular weightpolyethylene shrink pipe of the present invention can be appliedsuitably as a shrink pipe for covering for various rolls, pipes, steeltubes and so forth.

Further, a manufacturing method for an ultra-high molecular weightpolyethylene shrink pipe of the present invention can manufacture theultra-high molecular weight polyethylene shrink pipe described aboveefficiently.

Further, a manufacturing apparatus for an ultra-high molecular weightpolyethylene shrink pipe of the present invention can be used suitablyfor the manufacturing method for an ultra-high molecular weightpolyethylene shrink pipe described above.

According to a manufacturing method for an ultra-high molecular weightpolyethylene film of the present invention, an ultra-high molecularweight polyethylene film can be obtained which is suitable for anapplication for which a high degree of accuracy in dimension isrequired, because it is uniform in thickness and free from a folded markat both ear edges thereof comparing with a film obtained by aconventional blown film extrusion method. Particularly, since ultra highmolecular weight polyethylene is superior in abrasion resistance,self-lubrication and chemical resistance and particularly superior inabrasion resistance to fluorocarbon resins, the ultra-high molecularweight polyethylene film of the present invention is superior indurability. Consequently, the ultra-high molecular weight polyethylenefilm of the present invention can be applied suitably as a film forcovering for various rolls, pipes, steel tubes and so forth.

Further, a manufacturing apparatus for an ultra-high molecular weightpolyethylene film of the present invention can be used suitably for themanufacturing method for an ultra-high molecular weight polyethylenefilm described above.

An ultra-high molecular weight polyethylene thin-wall pipe of thepresent invention has a ratio of an outer diameter to a thickness of 10or more and is low in thermal shrinkage comparing with a conventionalthin-wall pipe. The ultra-high molecular weight polyethylene thin pipeis useful for a conveying pipe for powder making use of the abrasionresistance, self-lubrication and chemical resistance ultra-highmolecular weight polyethylene has, and can also be used suitably as atubular cover for a roll, a pipe or a steel tube, or as a guide railcover for a transport line or the like.

Further, a manufacturing method for an ultra-high molecular weightpolyethylene thin pipe of the present invention can manufacture theultra-high molecular weight polyethylene thin pipe at a high efficiency.

Further, a manufacturing apparatus for an ultra-high molecular weightpolyethylene thin pipe of the present invention can be used suitably forthe manufacturing method for an ultra-high molecular weight polyethylenethin pipe described above.

What is claimed is:
 1. A method of manufacturing an ultra-high molecularweight polyethylene thin-wall pipe, comprising the steps of:supplyingultra-high molecular weight polyethylene having an intrinsic viscosity(η) of 5.0 dl/g or more into a screw extruder, and melting and kneadingthe ultra-high molecular weight polyethylene; continuously extruding themolten substance of the ultra-high molecular weight polyethylene from adie having an L/D ratio at least 10, which includes an outer die, and aninner die connected to and rotated together with a screw of said screwextruder and disposed therein, to form a cylindrical extruder article;and diametrically expanding the cylindrical extruded article by means ofa tapered core connected to said inner ride through a shaft and not torotate with a shaft rotating together with the inner die, which includesa tapered portion and a cylindrical portion provided continuously tosaid tapered portion, and causing the ultra-high molecular weightpolyethylene to start to be cooled to solidify at the tapered portion orthe cylindrical portion of the tapered core.
 2. A method ofmanufacturing an ultra-high molecular weight polyethylene shrink pipe,comprising the steps of:supplying ultra-high molecular weightpolyethylene having an intrinsic viscosity (η) of 5.0 dl/g or more intoa screw extruder, and melting and kneading the ultra-high molecularweight polyethylene; continuously extruding the molten substance of theultra-high molecular weight polyethylene from a die having an L/D ratioat last 10, which includes an outer die connected to and rotatedtogether with a screw of said screw extruder and disposed therein, toform a cylindrical extruded article; diametrically expanding thecylindrical extruded article such that the inner diameter of a maximumdiametrically expanding portion may be 1.2 to 3.0 times the outerdiameter of said inner die, by means of a tapered core connected to saidinner die through a shaft and not rotated with a shaft rotating togetherwith the inner die, which includes a tapered portion and a cylindricalportion provided continuously to said tapered portion; taking up theextruded article at a taking up rate lower than five times the extrudingrate at said screw extruder, and causing the ultra-high molecularpolyethylene to start to be cooled to solidify at the tapered portion orthe cylindrical portion of said tapered core.
 3. A method ofmanufacturing an ultra-high molecular weight polyethylene film,comprising the steps of:supplying ultra-high molecular weightpolyethylene having an intrinsic viscosity (η) of 5.0 dl/g or more intoa screw extruder, and melting and kneading the ultra-high molecularweight polyethylene; continuously extruding the molten substance of theultra-high molecular weight polyethylene from a die having a L/D ratioof at least 10, which includes an outer die, and an inner die connectedto and rotated together with a screw of said screw extruder and disposedin the inside of the outer die, to form a cylindrical extruded article;diametrically expanding the cylindrical extruded article such that theinner diameter of a maximum diametrically expanding portion may be 3times or more than the outer diameter of said inner die, by means of atapered core connected to said inner die through a shaft and not rotatedwith a shaft rotating together with the inner die, which includes atapered portion and a cylindrical portion provided continuously to saidtapered portion; taking up the extruded article at a taking up ratethree times or higher than the extruding rate at said screw extruder;and causing the ultra-high molecular weight polyethylene to start to becooled to solidify at the tapered portion or the cylindrical portion ofthe tapered core.
 4. A method of manufacturing an ultra-high molecularweight polyethylene shrink pipe, comprising the steps of:supplyingultra-high molecular weight polyethylene having an intrinsic viscosity(η) of 5.0 dl/g or more into a screw extruder, and melting and kneadingthe ultra-high molecular weight polyethylene; continuously extruding themolten substance of the ultra-high molecular weight polyethylene from adie having a L/D ratio of at least 10, which includes an outer die, andan inner die connected to and rotated together with a screw of saidscrew extruder and disposed in the inside of the outer die, to form acylindrical extruded article; diametrically expanding the cylindricalextruded article such that the outer diameter of a maximum diametricallyexpanding portion may be 1.2 to 3.0 times the outer diameter of saidinner die, by means of a tapered core connected to said inner diethrough a shaft and not rotated with a shaft rotating together with theinner die, which includes a tapered portion and a cylindrical portionprovided continuously to said tapered portion; taking up the extrudedarticle at a taking up rate lower than five times the extruding rate atsaid screw extruder, and causing the ultra-high molecular weightpolyethylene to start to be cooled to solidify at said cylindricalportion of the tapered core.